Alex McColgan

This may be a coincidence.

Perhaps life did arise multiple times, but the life that arose first was more advanced and so outcompeted the newly formed simple bacteria into extinction.

Still, it means that life is either incredibly certain or a million to one.

Let's go with the more pessimistic number and see where that takes us.

FL equals 0.0001%.

We encounter the same problem for the arising of intelligence.

There are numerous examples of animals displaying forms of intelligence.

Octopi can open jars and solve puzzles, and some birds and apes can use tools or even use sign language.

Perhaps this proves that, given enough time, life always evolves into becoming more intelligent.

However, if we want to be strict about it, we could also accurately say that all the millions of species that have existed on the Earth, only one was intelligent enough for our purposes – us.

Which makes the odds seem very low for it happening.

Let's once again input our 1 million to 1 value for Fi, again just to be pessimistic.

In terms of how many become technologically advanced enough to start communicating, I think this number is likely much higher.

Although we only have one species to compare to again, it's worth noting that humans are unintentionally chatty with the universe, quite by accident.

Thanks to industry and transport, we are altering the chemical composition of our atmosphere, which is something an alien race could detect.

Certain molecules in our atmosphere are only there because they are man-made.

we also send signals out into space thanks to our radio signals and satellites.

Sometimes we even send signals out into the stars deliberately, such as the Arecibo message, which was broadcast from Earth in 1974, and contained information about human civilization and history, expressly so any aliens that heard it could learn about us.

Although these signals would not travel far on the grand cosmological scale of things before becoming dispersed and indistinguishable from background radiation, we would count as a communicating race.

So I'm going to predict this number as high.